1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting uplink control information by a user equipment to a base station.
2. Related Art
Standardization works of international mobile telecommunication (IMT)-advanced which is a next generation (i.e., post 3rd generation) mobile communication system are carried out in the international telecommunication union radio communication sector (ITU-R). The IMT-advanced aims at support of an Internet protocol (IP)-based multimedia service with a data transfer rate of 1 Gbps in a stationary or slowly moving state or 100 Mbps in a fast moving state.
3rd generation partnership project (3GPP) is a system standard satisfying requirements of the IMT-advanced, and prepares long term evolution (LTE)-advanced which is an improved version of LTE based on orthogonal frequency division multiple access (OFDMA)/single carrier-frequency division multiple access (SC-FDMA) transmission. The LTE-advanced is one of promising candidates for the IMT-advanced.
A downlink denotes a link through which a base station (BS) transmits a signal to a user equipment (UE). An uplink denotes a link through which the UE transmits a signal to the BS. The LTE supports the use of 4 transmit (Tx) antennas in the downlink and supports the use of only one Tx antenna in the uplink. This is because the UE uses one power amplifier (AMP). As such, since the number of available Tx antennas is different between the downlink and the uplink, a peak/average system throughput is asymmetrical between the downlink and the uplink. This is one of major demerits of the LTE.
In the LTE-A, transmission of an uplink signal by using a plurality of Tx antennas (e.g., 4 Tx antennas) in the uplink is taken into account to improve an uplink throughput. When the UE transmits the uplink signal to the BS by using the 4 Tx antennas, uplink control information may be transmitted in a piggyback manner in a data transfer region. Accordingly, there is a need for a method and apparatus for reliably transmitting the uplink control signal by the UE in multiple-antenna transmission.